CO/sub 2/ laser stabilization to 0.1-Hz level using external electrooptic modulation

We have developed a frequency stabilization scheme for CO/sub 2/ lasers using only external modulation via an electrooptic modulator (EOM). One of the two laser sidebands which are generated by the EOM and frequency-modulated is set in resonance with a Fabry-Perot cavity, itself filled with OsO/sub 4/ as an absorber. The saturation signal of an OsO/sub 4/ line detected in transmission of the Fabry-Perot cavity is used for stabilization. We obtained a stability of 0.1 Hz (/spl Delta//spl nu///spl nu/=3.5 10/sup -15/) on a 100-s time scale, and a reproducibility up to 10 Hz with the strongest OsO/sub 4/ reference lines. These results largely improve the performance of our previous setup for which modulation was applied through piezoelectric transducers. Further, the stabilized laser is not frequency-modulated and is easily tunable.